Browsing by Author "Martinez Pina, F"

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    Dynamic mechanical and dielectric relaxations in poly(dibenzyl itaconate) and poly(diethylphenyl itaconate)
    (ELSEVIER SCI LTD, 2000) Calleja, RD; Martinez Pina, F; Gargallo, L; Radic, D
    Dynamic mechanical and dielectric behaviour of poly(dibenzyl itaconate), and poly(diethylphenyl itaconate) were studied. The study was performed by determining the components of the complex relaxation modulus E* and the complex dielectric permittivity epsilon*. The results are compared with those previously reported for poly(benzyl methacrylate), poly(monobenzyl itaconate) and poly(monoethylphenyl itaconate). The results are discussed in terms of the effect of flexible spacer groups and of the different steric hindrance between mono and disubstituted polymers. (C) 1999 Elsevier Science Ltd. All rights reserved.
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    Dynamic mechanical and dielectric relaxations of poly(difluorobenzyl methacrylates)
    (WILEY-BLACKWELL, 2000) Diaz Calleja, R; Sanchis, MJ; Saiz, E; Martinez Pina, F; Miranda, R; Gargallo, L; Radic, D; Riande, E
    This work reports the mechanical and dielectric relaxation spectra of three difluorinated phenyl isomers of poly(benzyl methacrylate), specifically, poly(2,4-difluorobenzyl methacrylate), poly(2,5-difluorobenzyl methacrylate) and poly(2,6-difluorobenzyl methacrylate). The strength of the dielectric glass-rubber relaxation of the 2,6 difluorinated phenyl isomer is, respectively, nearly three and two times larger than the strengths of the 2,5 and 2,4 isomers. The 2,4 isomer presents a mechanical ct peak the intensity of which is nearly two times that of the other two isomers. Both the mechanical and dielectric relaxation spectra display a subglass process, called gamma relaxation, centered in the vicinity of -50 degrees C at 1 Hz and, in some cases, a subglass beta absorption is detected at higher temperature partially masked by the glass-rubber relaxation. The mean-square dipole moments per repeating unit, [mu 2]/x, measured at 25 degrees C in benzene solutions, are 2.5 D-2, 1.9 D-2, and 5.0 D-2 for poly(2,4-difluorobenzyl methacrylate), poly(2,5-difluorobenzyl methacrylate) and poly(2,6-difluorobenzyl methacrylate), respectively. These results, in conjunction with Onsager type equations, permit to conclude that auto and cross-correlation contributions to the dipolar correlation coefficient may have the same time-dependence. On the other hand, dipole intermolecular interactions, rather than differences in the flexibility of the chains, seem to be responsible for the relatively high calorimetric glass-transition temperature of the 2,6 diphenyl isomer, which is, respectively, nearly 36 degrees C and 32 degrees C above the T-g's of the 2,4 and 2,5 isomers. Molecular Mechanics calculations give a good account of the differences observed in the polarity of the polymers. (C) 2000 John Wiley & Sons, Inc.
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    N-vinylimidazole-N-vinyl-2-pyrrolidone copolymers. Part I. Reactivity ratios, solubility and viscosimetric study
    (JOHN WILEY & SONS LTD, 1998) Martinez Pina, F; Gargallo, L; Radic, D
    Copolymers of N-vinylimidazole M with N-vinyl-2-pyrrolidone (VP), (VI-co-VP) were obtained by radical polymerization using alpha,alpha'-azobisisobutyronitrile as initiator. The copolymers were characterized by H-1 NMR and viscosimetric measurements. The monomer reactivity ratios were estimated to be r(1) = 1.00 for VP and r(2) = 0.07 for VI by the Fineman-Ross and Kelen-Tudos linear procedures. These parameters were also estimated using a computer program based on a non-linear minimization algorithm (NLMA) starting from the values of r(1) and r(2) obtained by the linear procedures. All copolymers could be considered as random. The solubility in chloroform, n-butanol and n-propanol depends on the copolymer composition. Water, methanol and ethanol are solvents, irrespective of the copolymer compositions. The viscosimetric behaviour of unfractionated copolymers of one composition was studied in dilute solution in water (pH 2.0 and 6.0) at 0.01 M (NaCl) ionic strength and in methanol. (C) 1998 Society of Chemical Industry